The overall program, consisting of several projects, has two major objectives: 1. The design, synthesis and purification of new gamma ray emitting radiopharmaceuticals, which may have usefulness in localizing or in following the growth and metabolism of tumors. These will be based on several principles: inhibition of general metabolic events, close analogues of known metabolites, active-site directed enzyme inhibitors, and more distant analogues of metabolites which can be tagged with gamma ray labels. 2. These newly synthesized radiopharmaceuticals will be used to follow and quantify tumor growth and regression after chemotherapy or radiation therapy. Indeed, some of the new compounds may themselves have therapeutic usefulness.